Is it possible to use object motion to drive audio properties in Blender?
For anyone else interested in this, the following StackExchange post contains a script which does exactly what I need.
https://blender.stackexchange.com/a/66257/70741
Having never used drivers before, I found this an incredibly useful introduction to them, and I can see myself using them a lot in future - I am, by trade, a programmer, so it kind of suits my mindset I guess.
Basically just follow the instructions there to get the delta X,Y,Z between frames and drive some custom properties dX, dY, and dZ on the moving object - the linked discussion talks you through doing all of this.
Once you've done this, you can use the custom properties in turn to derive the distance of motion between frames as sqrt(dX*dX + dY*dY + dZ*dZ) and drive another custom property distance
Once you've done that, you can use the custom distance property to drive the volume of a speaker object (or whatever else) however you'd like. You can also easily calculate a speed value using the frame rate if you need it (distance was sufficient for me)
You'll likely need to tweak the resulting values to suit your requirements, but it's not that hard to do.
The adjustments are a little &quot;choppy&quot;, but I'm pretty sure that can be smoothed out by updating the script to track a moving average over several frames, rather than just between single frames (which I'll be experimenting with next).
Thanks to everyone who dropped by to help out!